Organic electroluminescence device

ABSTRACT

An organic electroluminescence device comprising a pair of electrodes and a layer of an organic light emitting medium disposed between the pair of electrodes, wherein the layer of an organic light emitting medium comprises a mixed layer comprising (A) at least one hole transporting compound and (B) at least one electron transporting compound, an energy gap of the hole transporting compound represented by Eg1 and an energy gap of the electron transporting compound represented by Eg2 satisfy a relation: Eg1&lt;Eg2. Electrons and holes are recombined in the layer of an organic light emitting medium and light is emitted. The organic electroluminescence device has a long life and emits light at a high efficiency.

TECHNICAL FIELD

[0001] The present invention relates to an organic electroluminescencedevice (hereinafter, “electroluminescence” will be referred to as EL)and, more particularly, to an organic EL device having a long life andemitting light at a high efficiency.

BACKGROUND ART

[0002] EL devices which utilize light emission under application of anelectric field show high self-distinguishability due to theself-emission and exhibit excellent impact resistance since they arecompletely solid devices. Therefore, EL devices have been attractingattention for application as light emitting devices in various types ofdisplay apparatus.

[0003] The EL devices include inorganic EL devices in which an inorganiccompound is used as the light emitting material and organic EL devicesin which an organic compound is used as the light emitting material.Organic EL devices have been extensively studied for practicalapplication as a light emitting device of the next generation becausethe applied voltage can be decreased to a great extent, the size of thedevice can be reduced easily, consumption of electric power is small,planar light emission is possible and three primary colors are easilyemitted.

[0004] As for the construction of the organic EL device, the basicconstruction comprises an anode/an organic light emitting layer/acathode. Constructions having a hole injecting and transporting layer oran electron injecting layer suitably added to the basic construction areknown. Examples of such constructions include the construction of ananode/a hole injecting and transporting layer/an organic light emittinglayer/a cathode and the construction of an anode/a hole injecting andtransporting layer/an organic light emitting layer/an electron injectinglayer/a cathode.

[0005] In the development of organic EL devices which can be practicallyapplied, various studies to obtain a light emitting element having along life and emits light at a high efficiency have been conducted.However, an element having a longer life and emits light at a higherefficiency is desired so that consumption of electric power can befurther reduced.

[0006] For example, in International Patent Application Laid-Open No.98/08360 and U.S. Pat. No. 5,853,905, elements in which a mixed layer ofan amine derivative having the electron transporting property and anenergy gap of 3 eV or greater and an aluminum complex of8-hydroxyquinoline (Alq) as an electron transporting compound is used asthe light emitting medium are disclosed. Since the energy gap of Alq is2.7 eV, holes and electrons are recombined in Alq having a lower energygap and light is emitted in this light emitting medium. Since Alq itselfhas a small quantum yield of fluorescence, the efficiency is enhanced byadding a light emitting dopant such as coumarine and rubrene.

[0007] However, the technology disclosed in the above references has adrawback in that the life of the device cannot be increased to thedesired value. In other words, in general, few organic materials whichsimultaneously achieve excellent transportation of electrons andexcellent durability under an electric current can be found. It isconfirmed that Alq is degraded when holes are injected into Alq althoughAlq exhibits excellent durability in transportation of electrons. In thecase of the above light emitting medium, the energy gap of the holetransporting compound Eg1 and the energy gap of the electrontransporting compound Eg2 has the relation: Eg1>Eg2. Therefore, holestend to be injected into Alq having a smaller energy gap and the life ofthe device cannot be increased to the desired value. Although it isknown that durability of Alq can be improved by addition of a lightemitting dopant such as coumarine and rubrene, further improvement hasbeen desired.

DISCLOSURE OF THE INVENTION

[0008] Under the above circumstances, the present invention has anobject of providing an organic EL device which has a longer life andemits light at a higher efficiency than those of conventional organic ELdevices.

[0009] As the result of intensive studies by the present inventors toachieve the above object, it was found that an organic EL device havinga longer life and emitting light at a higher efficiency than those ofconventional organic EL devices could be obtained when an organicelectroluminescence device comprising a layer of an organic lightemitting medium comprised a mixed layer comprising (A) at least one holetransporting compound and (B) at least one electron transportingcompound and an energy gap of the hole transporting compound representedby Eg1 was smaller than an energy gap of the electron transportingcompound represented by Eg2. The present invention has been completedbased on the knowledge.

[0010] The present invention provides an organic electroluminescencedevice comprising a pair of electrodes and a layer of an organic lightemitting medium disposed between the pair of electrodes, wherein thelayer of an organic light emitting medium comprises a mixed layercomprising (A) at least one compound selected from hole transportingcompounds and (B) at least one compound selected from electrontransporting compounds and an energy gap of the hole transportingcompound represented by Eg1 and an energy gap of the electrontransporting compound represented by Eg2 satisfy a relation: Eg1<Eg2.

THE MOST PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION

[0011] The present invention provides an organic electroluminescencedevice comprising a pair of electrodes and a layer of an organic lightemitting medium disposed between the pair of electrodes, wherein thelayer of an organic light emitting medium comprises a mixed layercomprising (A) at least one compound selected from hole transportingcompounds and (B) at least one compound selected from electrontransporting compounds and an energy gap of the hole transportingcompound represented by Eg1 and an energy gap of the electrontransporting compound represented by Eg2 satisfy a relation: Eg1<Eg2.

[0012] Due to this relation in the layer of an organic light emittingmedium, holes are transported with the hole transporting compound andelectrons are injected into the hole transporting compound in the areaof recombination. Light is emitted by recombination of the holes and theelectrons. Since injection of holes into the electron transportingcompound is suppressed, degradation of the electron transportingcompound is suppressed and the life of the device is extended. The holetransporting compound can also provide durability to the electroninjection.

[0013] It is preferable that the ionization energy of the holetransporting compound represented by IP1 and the ionization energy ofthe electron transporting compound represented by IP2 satisfy therelation: IP1≦IP2.

[0014] Due to this relation, holes are more easily injected into thelowest occupied orbital of the hole transporting compound from an outerlayer of the light emitting medium. The outer layer means a layer otherthan the layer of the light emitting medium such as the anode, a holeinjecting layer, a hole transporting layer and a buffer layer.

[0015] It is preferable that the electron affinity of the holetransporting compound represented by Af1 and the electron affinity ofthe electron transporting compound represented by Af2 satisfy arelation: Af1≦Af2. The electron affinities represented by Af1 and Af2are values of the energies of the lowest vacant orbitals based on theenergy level of an electron in the vacuum as the reference. Due to thisrelation, electrons are more easily injected into the lowest vacantorbital of the electron transporting compound from an outer layer of thelayer of the light emitting medium. The outer layer means a layer otherthan the layer of the light emitting medium such as the cathode, anelectron injecting layer, an electron transporting layer, a holearresting layer or a buffer layer. In this case, it is preferable thatΔEv given by ΔEv=IP2−IP1 and ΔEc given by ΔEc=Af2−AF1 satisfy arelation: ΔEv≧ΔEc. Due to this relation, electrons are more easilyinjected into the lowest vacant orbital of the hole transportingcompound through the electron transporting compound. On the other hand,injection of holes into the lowest vacant orbital of the electroninjecting compound is suppressed.

[0016] The electron affinity of the hole transporting compoundrepresented by Af1 and the electron affinity of the electrontransporting compound represented by Af2 may satisfy a relation:Af1>Af2. In this case, the hole transporting compound does notsubstantially transport electrons or the mobility of electrons with thehole transporting compound is smaller than the mobility of electronswith the electron transporting compound. In this the mobility ofelectrons with the electron transporting compound. In this case, it ispreferable that ΔEv given by ΔEv=IP2−IP1 and ΔEc′ given by ΔEc′=Af1−AF2satisfy a relation: ΔEv≧ΔEc′. Due to this relation, the trapping effectof the hole transporting compound decreases and electrons transportedwith the electron transporting compound can more easily reach the areaof recombination.

[0017] It is preferable that the hole transporting compound used in theorganic EL device of the present invention is an aromatic amine having acondensed cyclic structure.

[0018] It is preferable that the aromatic amine is represented by thefollowing general formula (1):

[0019] wherein Ar¹ to Ar⁴ each independently represent a substituted orunsubstituted aromatic hydrocarbon group having 6 to 40 carbon atoms ora substituted or unsubstituted aromatic heterocyclic group having 3 to40 carbon atoms, Y represents a substituted or unsubstituted aromaticresidue group having 2 to 60 carbon atoms, at least one of the groupsrepresented by Ar¹ to Ar⁴ and Y has a condensed cyclic group having 3 ormore rings and a substituent in the groups represented by Ar¹ to Ar⁴ andY may form a ring with two groups selected from the groups representedby Ar¹ to Ar⁴ and Y; or by the following general formula (2):

[0020] wherein Ar¹ to Ar⁶ each independently represent a substituted orunsubstituted aromatic hydrocarbon group having 6 to 40 carbon atoms ora substituted or unsubstituted aromatic heterocyclic group having 3 to40 carbon atoms, Z represents a substituted or unsubstituted aromaticresidue group having 3 to 60 carbon atoms, at least one of the groupsrepresented by Ar¹ to Ar⁶ and Z has a condensed cyclic group having 3 ormore rings and a substituent in the groups represented by Ar¹ to Ar⁶ andZ may form a ring with two groups selected from the groups representedby Ar¹ to Ar⁶ and Z.

[0021] In the above general formulae (1) and (2), examples of the groupsrepresented by Ar¹ to Ar⁶, Y and Z include aromatic residue groupsderived from anthracene, chrysene, fluorene, pyrene, perylene,naphthalene, pentacene, coronene, fluoranthene, pycene, rubicene andacenaphthofluoranthene.

[0022] It is preferable that the compounds represented by generalformulae (1) and (2) are compounds represented by any of the followinggeneral formulae (7) to (11).

[0023] In the above general formula (7), R⁸ to R¹⁹ each independentlyrepresent hydrogen atom, a halogen atom, hydroxyl group, a substitutedor unsubstituted amino group, nitro group, cyano group, a substituted orunsubstituted alkyl group having 1 to 30 carbon atoms, a substituted orunsubstituted alkenyl group having 2 to 30 carbon atoms, a substitutedor unsubstituted cycloalkyl group having 5 to 30 carbon atoms, asubstituted or unsubstituted alkoxyl group having 1 to 30 carbon atoms,a substituted or unsubstituted aromatic hydrocarbon group having 6 to 40carbon atoms, a substituted or unsubstituted aromatic heterocyclic grouphaving 3 to 40 carbon atoms, a substituted or unsubstituted aralkylgroup having 7 to 40 carbon atoms, a substituted or unsubstitutedaryloxyl group having 6 to 40 carbon atoms, a substituted orunsubstituted alkoxycarbonyl group having 2 to 40 carbon atoms orcarboxyl group. Two groups selected from the groups represented by R⁸ toR¹⁹ may form a ring and at least one of the groups represented by R⁸ toR¹⁹ is a diarylamino group represented by —NAr⁷Ar⁸. Ar⁷ and Ar⁸ eachindependently represent a substituted or unsubstituted aryl group having6 to 20 carbon atoms.

[0024] In the above general formula (8), R²¹ to R³⁸ each independentlyrepresent hydrogen atom, a halogen atom, hydroxyl group, a substitutedor unsubstituted amino group, nitro group, cyano group, a substituted orunsubstituted alkyl group having 1 to 30 carbon atoms, a substituted orunsubstituted alkenyl group having 2 to 30 carbon atoms, a substitutedor unsubstituted cycloalkyl group having 5 to 30 carbon atoms, asubstituted or unsubstituted alkoxyl group having 1 to 30 carbon atoms,a substituted or unsubstituted aromatic hydrocarbon group having 6 to 40carbon atoms, a substituted or unsubstituted aromatic heterocyclic grouphaving 3 to 40 carbon atoms, a substituted or unsubstituted aralkylgroup having 7 to 40 carbon atoms, a substituted or unsubstitutedaryloxyl group having 6 to 40 carbon atoms, a substituted orunsubstituted alkoxycarbonyl group having 2 to 40 carbon atoms orcarboxyl group. Two groups selected from the groups represented by R²¹to R³⁸ may form a ring and at least one of the groups represented by R²¹to R³⁸ is a diarylamino group represented by —NAr⁷Ar⁸. Ar⁷ and Ar⁸ eachindependently represent a substituted or unsubstituted aryl grouphaving. 6 to 20 carbon atoms.

[0025] In the above general formula (9), Te represents a teryleneresidue group, Ar⁹ and Ar¹⁰ each independently represent a substitutedor unsubstituted alkyl group having 1 to 30 carbon atoms, a substitutedor unsubstituted monocyclic group or a substituted or unsubstitutedcondensed polycyclic group having 6 to 40 carbon atoms and r representsan integer of 1 to 6.

[0026] In the above general formula (10), Ar¹¹ to Ar¹⁴ eachindependently represent a substituted or unsubstituted aryl group having6 to 16 carbon atoms and R⁴¹ to R⁴⁸ each independently representhydrogen atom, a halogen atom, hydroxyl group, a substituted orunsubstituted amino group, nitro group, cyano group, a substituted orunsubstituted alkyl group having 1 to 30 carbon atoms, a substituted orunsubstituted alkenyl group having 2 to 30 carbon atoms, a substitutedor unsubstituted cycloalkyl group having 5 to 30 carbon atoms, asubstituted or unsubstituted alkoxyl group having 1 to 30 carbon atoms,a substituted or unsubstituted aromatic hydrocarbon group having 6 to 40carbon atoms, a substituted or unsubstituted aromatic heterocyclic grouphaving 3 to 40 carbon atoms, a substituted or unsubstituted aralkylgroup having 7 to 40 carbon atoms, a substituted or unsubstitutedaryloxyl group having 6 to 40 carbon atoms, a substituted orunsubstituted alkoxycarbonyl group having 2 to 40 carbon atoms orcarboxyl group and two groups selected from the groups represented byR⁴¹ to R⁴⁸ may form a ring.

[0027] In the above general formula (11), Ar¹⁵ to Ar¹⁸ eachindependently represent a substituted or unsubstituted alkyl grouphaving 1 to 30 carbon atoms, a substituted or unsubstituted monocyclicgroup, a substituted or unsubstituted condensed polycyclic group having8 to 40 carbon atoms; an integral combination of Ar¹⁵ and Ar¹⁶ and anintegral combination of Ar¹⁷ and Ar¹⁸ each represent a condensedpolycyclic group having a nitrogen atom as a bonding atom; Q representsa divalent bonding group bonding a cyclic group or a plurality of cyclicgroups and may be substituted or unsubstituted; R⁵¹ to R⁶⁶ eachindependently represent hydrogen atom, a halogen atom, hydroxyl group, asubstituted or unsubstituted amino group, nitro group, cyano group, asubstituted or unsubstituted alkyl group having 1 to 30 carbon atoms, asubstituted or unsubstituted alkenyl group having 2 to 30 carbon atoms,a substituted or unsubstituted cycloalkyl group having 5 to 30 carbonatoms, a substituted or unsubstituted alkoxyl group having 1 to 30carbon atoms, a substituted or unsubstituted a romatic hydrocarbon grouphaving 6 to 40 carbon atoms, a substituted or unsubstituted aromaticheterocyclic group having 3 to 40 carbon atoms, a substituted orunsubstituted aralkyl group having 7 to 40 carbon atoms, a substitutedor unsubstituted aryloxyl group having 6 to 40 carbon atoms, asubstituted or unsubstituted alkoxycarbonyl group having 2 to 40 carbonatoms or carboxyl group; and two groups selected from the groupsrepresented by R⁵¹ to R⁶⁶ may form a ring.

[0028] The aromatic amine compound, the aromatic diamine compound andthe aromatic triamine compound used in the present invention arecompounds having structures represented by the above general formulae(1), (2) and (7) to (11). In each general formula, preferable examplesof the substituent include halogen atoms, hydroxyl group, substitutedand unsubstituted amino groups, nitro group, cyano group, substitutedand unsubstituted alkyl groups, substituted and unsubstituted alkenylgroups, substituted and unsubstituted cycloalkyl groups, substituted andunsubstituted alkoxyl groups, substituted and unsubstituted aromatichydrocarbon groups, substituted and unsubstituted aromatic heterocyclicgroups, substituted and unsubstituted aralkyl groups, substituted andunsubstituted aryl groups, substituted and unsubstituted aryloxylgroups, substituted or unsubstituted alkoxycarbonyl groups and carboxylgroup.

[0029] Examples of the substituted and unsubstituted alkyl groupsinclude methyl group, ethyl group, propyl group, isopropyl group,n-butyl group, s-butyl group, isobutyl group, t-butyl group, n-pentylgroup, n-hexyl group, n-heptyl group, n-octyl group, hydroxymethylgroup, 1-hydroxyethyl group, 2-hydroxyethyl group, 2-hydroxyisobutylgroup, 1,2-dihydroxyethyl group, 1,3-dihydroxyisopropyl group,2,3-dihydroxy-t-butyl group, 1,2,3-trihydroxypropyl group, chloromethylgroup, 1-chloroethyl group, 2-chloroethyl group, 2-chloroisobutyl group,1,2-dichloroethyl group, 1,3-dichloroisopropyl group,2,3-dichloro-t-butyl group, 1,2,3-trichloropropyl group, bromomethylgroup, 1-bromoethyl group, 2-bromoethyl group, 2-bromoisobutyl group,1,2-dibromoethyl group, 1,3-dibromoisopropyl group, 2,3-dibromo-t-butylgroup, 1,2,3-tribromopropyl group, iodomethyl group, 1-iodoethyl group,2-iodoethyl group, 2-iodoisobutyl group, 1,2-diiodoethyl group,1,3-diiodoisopropyl group, 2,3-diiodo-t-butyl group, 1,2,3-triiodopropylgroup, aminomethyl group, 1-aminoethyl group, 2-aminoethyl group,2-aminoisobutyl group, 1,2-diaminoethyl group, 1,3-diaminoisopropylgroup, 2,3-diamino-t-butyl group, 1,2,3-triaminopropyl group,cyanomethyl group, 1-cyanoethyl group, 2-cyanoethyl group,2-cyanoisobutyl group, 1,2-dicyanoethyl group, 1,3-dicyanoisopropylgroup, 2,3-dicyano-t-butyl group, 1,2,3-tricyanopropyl group,nitromethyl group, 1-nitroethyl group, 2-nitroethyl group,2-nitroisobutyl group, 1,2-dinitroethyl group, 1,3-dinitroisopropylgroup, 2,3-dinitro-t-butyl group and 1,2,3-trinitropropyl group.

[0030] Examples of the substituted and unsubstituted alkenyl groupsinclude vinyl group, allyl group, 1-butenyl group, 2-butenyl group,3-butenyl group, 1,3-butadienyl group, 1-methylvinyl group, styrylgroup, 2,2-diphenylvinyl group, 1,2-diphenylvinyl group, 1-methylallylgroup, 1,1-dimethylallyl group, 2-methylallyl group, 1-phenylallylgroup, 2-phenylallyl group, 3-phenylallyl group, 3,3-diphenylallylgroup, 1,2-dimethylallyl group, 1-phenyl-1-butenyl group and3-phenyl-1-butenyl group.

[0031] Examples of the substituted and unsubstituted cycloalkyl groupsinclude cyclopropyl group, cyclobutyl group, cyclopentyl group,cyclohexyl group and 4-methylcyclohexyl group.

[0032] The substituted and unsubstituted alkoxyl groups are representedby —OY¹. Examples of the group represented by Y¹ include methyl group,ethyl group, propyl group, isopropyl group, n-butyl group, s-butylgroup, isobutyl group, t-butyl group, n-pentyl group, n-hexyl group,n-heptyl group, n-octyl group, hydroxymethyl group, 1-hydroxyethylgroup, 2-hydroxyethyl group, 2-hydroxyisobutyl group, 1,2-dihydroxyethylgroup, 1,3-dihydroxyisopropyl group, 2,3-dihydroxy-t-butyl group,1,2,3-trihydroxypropyl group, chloromethyl group, 1-chloroethyl group,2-chloroethyl group, 2-chloroisobutyl group, 1,2-dichloroethyl group,1,3-dichloroisopropyl group, 2,3-dichloro-t-butyl group,1,2,3-trichloropropyl group, bromomethyl group, 1-bromoethyl group,2-bromoethyl group, 2-bromoisobutyl group, 1,2-dibromoethyl group,1,3-dibromoisopropyl group, 2,3-dibromo-t-butyl group,1,2,3-tribromopropyl group, iodomethyl group, 1-iodoethyl group,2-iodoethyl group, 2-iodoisobutyl group, 1,2-diiodoethyl group,1,3-diiodoisopropyl group, 2,3-diiodo-t-butyl group, 1,2,3-triiodopropylgroup, aminomethyl group, 1-aminoethyl group, 2-aminoethyl group,2-aminoisobutyl group, 1,2-diaminoethyl group, 1,3-diaminoisopropylgroup, 2,3-diamino-t-butyl group, 1,2,3-triaminopropyl group,cyanomethyl group, 1-cyanoethyl group, 2-cyanoethyl group,2-cyanoisobutyl group, 1,2-dicyanoethyl group, 1,3-dicyanoisopropylgroup, 2,3-dicyano-t-butyl group, 1,2,3-tricyanopropyl group,nitromethyl group, 1-nitroethyl group, 2-nitroethyl group,2-nitroisobutyl group, 1,2-dinitroethyl group, 1,3-dinitroisopropylgroup, 2,3-dinitro-t-butyl group and 1,2,3-trinitropropyl group.

[0033] Examples of the substituted and unsubstituted aromatichydrocarbon groups include phenyl group, 1-naphthyl group, 2-naphthylgroup, 1-anthryl group, 2-anthryl group, 9-anthryl group, 1-phenanthrylgroup, 2-phenanthryl group, 3-phenanthryl group, 4-phenanthryl group,9-phenanthryl group, 1-naphthacenyl group, 2-naphthacenyl group,9-naphthacenyl group, 1-pyrenyl group, 2-pyrenyl group, 4-pyrenyl group,2-biphenylyl group, 3-biphenylyl group, 4-biphenylyl group,p-terphenyl-4-yl group, p-terphenyl-3-yl group, p-terphenyl-2-yl group,m-terphenyl-4-yl group, m-terphenyl-3-yl group, m-terphenyl-2-yl group,o-tolyl group, m-tolyl group, p-tolyl group, p-t-butylpheny group,p-(2-phenylpropyl)phenyl group, 3-methyl-2-naphthyl group,4-methyl-1-naphthyl group, 4-methyl-1-anthryl group, 4′-methylbiphenylylgroup and 4″-t-butyl-p-terphenyl-4-yl group.

[0034] Examples of the substituted and unsubstituted aromaticheterocyclic groups include 1-pyrrolyl group, 2-pyrrolyl group,3-pyrrolyl group, pyradinyl group, 2-pyridinyl group, 3-pyridinyl group,4-pyridinyl group, 1-indolyl group, 2-indolyl group, 3-indolyl group,4-indolyl group, 5-indolyl group, 6-indolyl group, 7-indolyl group,1-isoindolyl group, 2-isoindolyl group, 3-isoindolyl group, 4-isoindolylgroup, 5-isoindolyl group, 6-isoindolyl group, 7-isoindolyl group,2-furyl group, 3-furyl group, 2-benzofuranyl group, 3-benzofuranylgroup, 4-benzofuranyl group, 5-benzofuranyl group, 6-benzofuranyl group,7-benzofuranyl group, l-isobenzofuranyl group, 3-isobenzofuranyl group,4-isobenzofuranyl group, 5-isobenzofuranyl group, 6-isobenzofuranylgroup, 7-isobenzofuranyl group, 2-quinolyl group, 3-quinolyl group,4-quinolyl group, 5-quinolyl group, 6-quinolyl group, 7-quinolyl group,8-quinolyl group, 1-isoquinolyl group, 3-isoquinolyl group,4-isoquinolyl group, 5-isoquinolyl group, 6-isoquinolyl group,7-isoquinolyl group, 8-isoquinolyl group, 2-quinoxanyl group,5-quinoxanyl group, 6-quinoxanyl group, 1-carbazolyl group, 2-carbazolylgroup, 3-carbazolyl group, 4-carbazolyl group, 9-carbazolyl group,1-phenanthridinyl group, 2-phenanthridinyl group, 3-phenanthridinylgroup, 4-phenanthridinyl group, 6-phenanthridinyl group,7-phenanthridinyl group, 8-phenanthridinyl group, 9-phenanthridinylgroup, 10-phenanthridinyl group, 1-acridinyl group, 2-acridinyl group,3-acridinyl group, 4-acridinyl group, 9-acridinyl group, phenanthrolylgroup, 2-thienyl group, 3-thienyl group, 2-methylpyrrol-1-yl group,2-methylpyrrol-3-yl group, 2-methylpyrrol-4-yl group,2-methylpyrrol-5-yl group, 3-methylpyrrol-1-yl group,3-methylpyrrol-2-yl group, 3-methylpyrrol-4-yl group,3-methyl-pyrrol-5-yl group, 2-t-butylpyrrol-4-yl group,3-(2-phenylpropyl)pyrrol-1-yl group, -2-methyl-1-indolyl group,4-methyl-1-indolyl group, 2-methyl-3-indolyl group, 4-methyl-3-indolylgroup, 2-t-butyl-1-indolyl group, 4-t-butyl-1-indolyl group,2-t-butyl-3-indolyl group and 4-t-butyl-3-indolyl group.

[0035] Examples of the substituted and unsubstituted aralkyl groupsinclude benzyl group, 1-phenylethyl group, 2-phenylethyl group,1-phenylisopropyl group, 2-phenylisopropyl group, phenyl-t-butyl group,α-naphthylmethyl group, 1-α-naphthylethyl group, 2-α-naphthylethylgroup, 1-α-naphthylisopropyl group, 2-α-naphthylisopropyl group,13-naphthylmethyl group, 1-β-naphthylethyl group, 2-β-naphthylethylgroup, 1-β-naphthylisopropyl group, 2-β-naphthylisopropyl group,1-pyrrolylmethyl group, 2-(1-pyrrolyl)ethyl group, p-methylbenzyl group,m-methylbenzyl group, o-methylbenzyl group, p-chlorobenzyl group,m-chlorobenzyl group, o-chlorobenzyl group, p-bromobenzyl group,m-bromobenzyl group, o-bromobenzyl group, p-iodobenzyl group,m-iodobenzyl group, o-iodobenzyl group, p-hydroxybenzyl group,m-hydroxybenzyl group, o-hydroxybenzyl group, p-aminobenzyl group,m-aminobenzyl group, o-aminobenzyl group, p-nitrobenzyl group,m-nitrobenzyl group, o-nitrobenzyl group, p-cyanobenzyl group,m-cyanobenzyl group, o-cyanobenzyl group, 1-hydroxy-2-phenylisopropylgroup and 1-chloro-2-phenylisopropyl group.

[0036] Examples of the substituted and unsubstituted aryl groups includephenyl group, 1-naphthyl group, 2-naphthyl group, 1-anthryl group,2-anthryl group, 9-anthryl group, 1-phenanthryl group, 2-phenanthrylgroup, 3-phenanthryl group, 4-phenanthryl group, 9-phenanthryl group,1-naphthacenyl group, 2-naphthacenyl group, 9-naphthacenyl group,1-pyrenyl group, 2-pyrenyl group, 4-pyrenyl group, 2-biphenylyl group,3-biphenylyl group, 4-biphenylyl group, p-terphenyl-4-yl group,p-terphenyl-3-yl group, p-terphenyl-2-yl group, m-terphenyl-4-yl group,m-terphenyl-3-yl group, m-terphenyl-2-yl group, o-tolyl group, m-tolylgroup, p-tolyl group, p-t-butylpheny group, p-(2-phenylpropyl)phenylgroup, 3-methyl-2-naphthyl group, 4-methyl-1-naphthyl group,4-methyl-1-anthryl group, 4′-methylbiphenylyl group,4′-t-butyl-p-terphenyl-4-yl group, 2-pyrrolyl group, 3-pyrrolyl group,pyradinyl group, 2-pyridinyl group, 3-pyridinyl group, 4-pyridinylgroup, 2-indolyl group, 3-indolyl group, 4-indolyl group, 5-indolylgroup, 6-indolyl group, 7-indolyl group, 1-isoindolyl group,3-isoindolyl group, 4-isoindolyl group, 5-isoindolyl group, 6-isoindolylgroup, 7-isoindolyl group, 2-furyl group, 3-furyl group, 2- benzofuranylgroup, 3-benzofuranyl group, 4-benzofuranyl group, 5-benzofuranyl group,6-benzofuranyl group, 7-benzofuranyl group, 1-isobenzofuranyl group,3-isobenzofuranyl group, 4-isobenzofuranyl group, 5-isobenzofuranylgroup, 6-isobenzofuranyl group, 7-isobenzofuranyl group, 2-quinolylgroup, 3-quinolyl group, 4-quinolyl group, 5-quinolyl group, 6-quinolylgroup, 7-quinolyl group, 8-quinolyl group, 1-isoquinolyl group,3-isoquinolyl group, 4-isoquinolyl group, 5-isoquinolyl group,6-isoquinolyl group, 7-isoquinolyl group, 8-isoquinolyl group,2-quinoxanyl group, 5-quinoxanyl group, 6-quinoxanyl group, 1-carbazolylgroup, 2-carbazolyl group, 3-carbazolyl group, 4-carbazolyl group,1-phenanthridinyl group, 2-phenanthridinyl group, 3-phenanthridinylgroup, 4-phenanthridinyl group, 6-phenanthridinyl group,7-phenanthridinyl group, 8-phenanthridinyl group, 9-phenanthridinylgroup, 1-acridinyl group, 2-acridinyl group, 3-acridinyl group,4-acridinyl group, 9-acridinyl group, phenanthrolyl group, 2-thienylgroup, 3-thienyl group, 2-methylpyrrol-1-yl group, 2-methylpyrrol-3-ylgroup, 2-methylpyrrol-4-yl group, 2-methyl-pyrrol-5-yl group,3-methylpyrrol-1-yl group, 3-methylpyrrol-2-yl group,3-methylpyrrol-4-yl group, 3-methylpyrrol-5-yl group,2-t-butylpyrrol-4-yl group, 3-(2-phenylpropyl)pyrrol-1-yl group,2-methyl-1-indolyl group, 4-methyl-1-indolyl group, 2-methyl-3-indolylgroup, 4-methyl-3-indolyl group, 2-t-butyl-1-indolyl group,4-t-butyl-1-indolyl group, 2-t-butyl-3-indolyl group and4-t-butyl-3-indolyl group.

[0037] The substituted and unsubstituted aryloxy groups are representedby —OZ¹. Examples of the group represented by Zl include phenyl group,1-naphthyl group, 2-naphthyl group, 1-anthryl group, 2-anthryl group,9-anthryl group, 1-phenanthryl group, 2-phenanthryl group, 3-phenanthrylgroup, 4-phenanthryl group, 9-phenanthryl group, 1-naphthacenyl group,2-naphthacenyl group, 9-naphthacenyl group, 1-pyrenyl group, 2-pyrenylgroup, 4-pyrenyl group, 2-biphenylyl group, 3-biphenylyl group,4-biphenylyl group, p-terphenyl-4-yl group, p-terphenyl-3-yl group,p-terphenyl-2-yl group, m-terphenyl-4-yl group, m-terphenyl-3-yl group,m-terphenyl-2-yl group, o-tolyl group, m-tolyl group, p-tolyl group,p-t-butylpheny group, p-(2-phenylpropyl)phenyl group,3-methyl-2-naphthyl group, 4-methyl-1-naphthyl group, 4-methyl-1-anthrylgroup, 4′-methylbiphenylyl group, 4″-t-butyl-p-terphenyl-4-yl group,2-pyrrolyl group, 3-pyrrolyl group, pyradinyl group, 2-pyridinyl group,3-pyridinyl group, 4-pyridinyl group, 2-indolyl group, 3-indolyl group,4-indolyl group, 5-indolyl group, 6-indolyl group, 7-indolyl group,1-isoindolyl group, 3-isoindolyl group, 4-isoindoiyl group, 5-isoindolylgroup, 6-isoindolyl group, 7-isoindolyl group, 2-furyl group, 3-furylgroup, 2-benzofuranyl group, 3-benzofuranyl group, 4-benzofuranyl group,5-benzofuranyl group, 6-benzofuranyl group, 7-benzofuranyl group,1-isobenzofuranyl group, 3-isobenzofuranyl group, 4-isobenzofuranylgroup, 5-isobenzofuranyl group, 6-isobenzofuranyl group,7-isobenzofuranyl group, 2-quinolyl group, 3-quinolyl group, 4-quinolylgroup, 5-quinolyl group, 6-quinolyl group, 7-quinolyl group, 8-quinolylgroup, 1-isoquinolyl group, 3-isoquinolyl group, 4-isoquinolyl group,5-isoquinolyl group, 6-isoquinolyl group, 7-isoquinolyl group,8-isoquinolyl group, 2-quinoxanyl group, 5-quinoxanyl group,6-quinoxanyl group, 1-carbazolyl group, 2-carbazolyl group, 3-carbazolylgroup, 4-carbazolyl group, 1-phenanthridinyl group, 2-phenanthridinylgroup, 3-phenanthridinyl group, 4-phenanthridinyl group,6-phenanthridinyl group, 7-phenanthridinyl group, 8-phenanthridinylgroup, 9-phenanthridinyl group, 1-acridinyl group, 2-acridinyl group,3-acridinyl group, 4-acridinyl group, 9-acridinyl group, phenanthrolylgroup, 2-thienyl group, 3-thienyl group, 2-methylpyrrol-1-yl group,2-methylpyrrol-3-yl group, 2-methylpyrrol-4-yl group,2-methylpyrrol-5-yl group, 3-methylpyrrol-1-yl group,3-methylpyrrol-2-yl group, 3-methylpyrrol-4-yl group,3-methyl-pyrrol-5-yl group, 2-t-butylpyrrol-4-yl group,3-(2-phenylpropyl)pyrrol-1-yl group, 2-methyl-1-indolyl group,4-methyl-1-indolyl group, 2-methyl-3-indolyl group, 4-methyl-3-indolylgroup, 2-t-butyl-1-indolyl group, 4-t-butyl-1-indolyl group,2-t-butyl-3-indolyl group and 4-t-butyl-3-indolyl group.

[0038] The substituted and unsubstituted alkoxycarbonyl groups arerepresented by —COOY². Examples of the group represented by Y² includemethyl group, ethyl group, propyl group, isopropyl group, n-butyl group,s-butyl group, isobutyl group, t-butyl group, n-pentyl group, n-hexylgroup, n-heptyl group, n-octyl group, hydroxymethyl group,1-hydroxyethyl group, 2-hydroxyethyl group, 2-hydroxyisobutyl group,1,2-dihydroxyethyl group, 1,3-dihydroxyisopropyl group,2,3-dihydroxy-t-butyl group, 1,2,3-trihydroxypropyl group, chloromethylgroup, 1-chloroethyl group, 2-chloroethyl group, 2-chloroisobutyl group,1,2-dichloroethyl group, 1,3-dichloroisopropyl group,2,3-dichloro-t-butyl group, 1,2,3-trichloropropyl group, bromomethylgroup, 1-bromoethyl group, 2-bromoethyl group, 2-bromoisobutyl group,1,2-dibromoethyl group, 1,3-dibromoisopropyl group, 2,3-dibromo-t-butylgroup, 1,2,3-tribromopropyl group, iodomethyl group, 1-iodoethyl group,2-iodoethyl group, 2-iodoisobutyl group, 1,2-diiodoethyl group,1,3-diiodoisopropyl group, 2,3-diiodo-t-butyl group, 1,2,3-triiodopropylgroup, aminomethyl group, 1-aminoethyl group, 2-aminoethyl group,2-aminoisobutyl group, 1,2-diaminoethyl group, 1,3-diaminoisopropylgroup, 2,3-diamino-t-butyl group, 1,2,3-triaminopropyl group,cyanomethyl group, 1-cyanoethyl group, 2-cyanoethyl group,2-cyanoisobutyl group, 1,2-dicyanoethyl group, 1,3-dicyanoisopropylgroup, 2,3-dicyano-t-butyl group, 1,2,3-tricyanopropyl group,nitromethyl group, 1-nitroethyl group, 2-nitroethyl group,2-nitroisobutyl group, 1,2-dinitroethyl group, 1,3-dinitroisopropylgroup, 2,3-dinitro-t-butyl group and 1,2,3-trinitropropyl group.

[0039] It is preferable that the electron transporting compound used inthe organic EL device of the present invention is a heterocycliccompound having a nitrogen atom or a complex having a nitrogen atom andmore preferably a complex having a nitrogen atom. The heterocycliccompound having a nitrogen atom and the complex having a nitrogen atomare preferable since these compounds have electron affinities as greatas 2.7 eV or greater and mobilities of electrons as great as 1×10⁻⁶cm²/V·S or greater.

[0040] Examples of the heterocyclic compound having a nitrogen atominclude oxadiazole derivatives such as2-(4-biphenylyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole andbis[2-(4-tert-butyl-phenyl)-1,3,4-oxadiazole]-m-phenylene, triazolederivatives and quinoxalinequinoline derivatives.

[0041] It is preferable that the complex having a nitrogen atom isrepresented by the following general formula (3):

M-A_(m)B_(n)   (3)

[0042] wherein M represents a monovalent to trivalent metal, Arepresents a ligand having a nitrogen atom, B represents a ligand havingno nitrogen atoms, m represents an integer of 1 to 4, n represents aninteger of 0 to 2 and integers represented by m and n satisfy m+n≦4.

[0043] Examples of the metal represented by M include Li, Na, Cs, Be,Mg, Ca, Ba, Zn, Cd, Al, Ga, In and Yb. Among these metals, Al, Be and Gaare preferable.

[0044] Examples of the ligand represented by A include ligands based onquinolinol and ligands based on benzoquinolinol.

[0045] Examples of the complex having a nitrogen atom include complexesrepresented by the following general formulae (i) to (iii):

[0046] (i) M⁺A or M⁺A′ (M⁺ representing a monovalent metal ion)

[0047] (ii) M²⁺A₂, M²⁺AA′ or M²⁺A′₂ (M²⁺ representing a divalent metalion)

[0048] (iii) M³⁺A₃, M³⁺A₂A′, M³⁺AA′₂ or M³⁺A′₃ (M³⁺ representing atrivalent metal ion)

[0049] Examples of the ligands represented by A and A′ include ligandsrepresented by the following general formula (iv). The ligandsrepresented by A and A′ may the same with or different from each other.Substituents in the ligands represented by A and A′ may be the same withor different from each other. Examples of the substituent include alkylgroups, alkoxyl groups, aryloxyl groups and aryl groups.

[0050] In the above general formula (iv), A¹ and A² each independentlyrepresent a substituted or unsubstituted aromatic cyclic structure andmay represent the same structure or different structures.

[0051] Further examples of the ligands represented by A and A′ includeligands represented by the following general formulae:

[0052] In the above formulae, D represents an atom selected from Si, Geand Sn and Ar²¹ to Ar²⁵ each independently represent an aromatichydrocarbon group or an aromatic heterocyclic group which may havesubstituents.

[0053] Further examples of the ligands represented by A and A′ includebenzoazoles such as derivatives of benzimidazole, benzothiazole andbenzoxazole.

[0054] Among the above ligands having a nitrogen atom which arerepresented by A and A′, ligands represented by the following generalformula (4) are preferable:

[0055] wherein R² to R⁷ each independently represent hydrogen atom, ahalogen atom, hydroxyl group, a substituted or unsubstituted aminogroup, nitro group, cyano group, a substituted or unsubstituted alkylgroup having 1 to 30 carbon atoms, a substituted or unsubstitutedalkenyl group having 2 to 30 carbon atoms, a substituted orunsubstituted cycloalkyl group having 5 to 30 carbon atoms, asubstituted or unsubstituted alkoxyl group having 1 to 30 carbon atoms,a substituted or unsubstituted aromatic hydrocarbon group having 6 to 40carbon atoms, a substituted or unsubstituted aromatic heterocyclic grouphaving 3 to 40 carbon atoms, a substituted or unsubstituted aralkylgroup having 7 to 40 carbon atoms, a substituted or unsubstitutedaryloxyl group having 6 to 40 carbon atoms, a substituted orunsubstituted alkoxycarbonyl group having 2 to 40 carbon atoms orcarboxyl group and two groups selected from the groups represented by R²to R⁷ may form a ring.

[0056] Examples of the complex having ligands having a nitrogen atom asthe complex having a nitrogen atom include complexes having ligandshaving a nitrogen atom which are derived from 8-quinolinol or derivativethereof such as tris(8-quinolinolato)aluminum,bis(8-quinolinolato)magnesium, bis-(benzo(f)-8-quinolinolato)zinc, bis(2-methyl-8-quinolinolato)aluminum oxide, tris(8-quinolinolato)indium,tris(5-methyl-8-quinolinolato)aluminum, 8-quinolinolatolithium,tris(5-methyl-8-quinolinolato)gallium,bis(5-chloro-8-quinolinolato)calcium,5,7-dichloro-8-8-quinilinolatoaluminum,tris(5,7-dibromo-8-hydroxyquinolinolato)aluminum andpoly[zinc(II)-bis(8-hydroxy-5-quinolinyl)methane].

[0057] Examples of the complex having a ligand having a nitrogen atomand a ligand having no nitrogen atoms includebis(2-methyl-8-quinolinolato)(phenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(ortho-cresolato)aluminum(III),bis(2-methyl-8-quinolinolato)(metacresolato)aluminum(III),bis(2-methyl-8-quinolinolato)(para-cresolato)aluminum(III),bis(2-methyl-8-quinolinolato)(ortho-phenylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(meta-phenylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(para-phenylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(2,3-dimethylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(2,6-dimethylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(3,4-dimethylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(3,5-dimethylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(3,5-di-tert-butylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(2,6-diphenylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(2,4,6-triphenylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(2,3,6-trimethylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(2,3,5,6-tetramethylphenolato)aluminum(III),bis(2-methyl-8-quinolinolato)(1-naphtholato)aluminum(III),bis(2-methyl-8-quinolinolato)(2-naphtholato)aluminum(III),bis(2,4-dimethyl-8-quinolinolato)(ortho-phenylphenolato)aluminum(III),bis(2,4-dimethyl-8-quinolinolato)(para-phenylphenolato)aluminum(III),bis(2,4-dimethyl-8-quinolinolato)(meta-phenylphenolato)aluminum(III),bis(2,4-dimethyl-8-quinolinolato)(3,5-dimethylphenolato)aluminum(III),bis(2,4-dimethyl-8-quinolinolato)(3,5-di-tert-butylphenolato)aluminum(III),bis(2-methyl-4-ethyl-8-quinolinolato)(para-cresolato)aluminum(III),bis(2-methyl-4-methoxy-8-quinolinolato)(para-phenylphenolato)aluminum(III),bis(2-methyl-5-cyano-8-quinolinolato)(ortho-cresolato)aluminum(III),bis(2-methyl-6-trifluoromethyl-8-quinolinolato)(2-naphtholato)aluminum(III),bis(2-methyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(2-methyl-8-quinolinolato)-aluminum(III),bis(2,4-dimethyl-8-quinolinolato)-aluminum(III)-μ-oxo-bis(2,4-dimethyl-8-quinolinolato)aluminum(III),bis(4-ethyl-2-methyl-8-quinohnolato)aluminum(III)-μ-oxo-bis(4-ethyl-2-methyl-8-quinolinolato)-aluminum(III),bis(2-methyl-4-mothoxyquinolinolato)-aluminum(III)-μ-oxo-bis(2-methyl-4-methoxyquinolinolato)aluminum(III),bis(5-cyano-2-methyl-8-quinolinolato)aluminumIII)-μ-oxo-bis(5-cyano-2-methyl-8-quinolinolato)aluminum(III)andbis(2-methyl-5-trifluoromethyl-8-quinolinolato)aluminum(III)-μ-oxo-bis(2-methyl-5-trifluoromethyl-8-quinolinolato)aluminum(III).

[0058] The electron transporting compound used in the organic EL deviceof the present invention may be an anthracene derivative represented bythe following general formula (5):

A¹-L-A²   (5)

[0059] wherein A¹ and A² each independently represent a substituted orunsubstituted monophenylanthryl group or a substituted or unsubstituteddiphenylanthryl group and may represent the same group or differentgroups and L represents a single bond or a divalent bonding group; or bythe following general formula (6):

A³-An-A⁴   (6)

[0060] wherein An represents a substituted or unsubstituted anthraceneresidue group and A³ and A⁴ each independently represent a substitutedor unsubstituted monovalent condensed aromatic cyclic group having 10 to40 carbon atoms or a substituted or unsubstituted aryl group having nocondensed cyclic structures and having 12 to 40 carbon atoms and mayrepresent the same group or different groups.

[0061] Examples of the substituent in general formulae (5) and (6)include alkyl groups having 1 to 6 carbon atoms, cycloalkyl groupshaving 3 to 6 carbon atoms, alkoxyl groups having 1 to 6 carbon atoms,aryloxyl groups having 5 to 18 carbon atoms, aralkyloxyl groups having 7to 18 carbon atoms, amino groups substituted with aryl groups having 5to 16 carbon atoms, nitro group, cyano group, ester groups having 1 to 6carbon atoms, halogen atoms and alkenyl groups.

[0062] Examples of the alkyl group having 1 to 6 carbon atoms includemethyl group, ethyl group, propyl group, isopropyl group, butyl group,isobutyl group, sec-butyl group, tert-butyl group, various types ofpentyl groups and various types of hexyl groups.

[0063] Examples of the cycloalkyl group having 3 to 6 carbon atomsinclude cyclopropyl group, cyclobutyl group, cyclopentyl group andcyclohexyl group.

[0064] Examples of the alkoxyl group having 1 to 6 carbon atoms includemethoxyl group, ethoxyl group, propoxyl group, isopropoxyl group,butoxyl group, isobutoxyl group, sec-butoxyl group, tert-butoxyl group,various types of pentyloxyl groups and various types of hexyloxylgroups.

[0065] Examples of the aryloxyl group having 5 to 18 carbon atomsinclude phenoxyl group, tolyloxyl group and naphthyloxyl group.

[0066] Examples of the aralkyloxyl group having 7 to 18 carbon atomsinclude benzyloxyl group, phenetyloxyl group and naphthylmethoxyl group.

[0067] Examples of the amino group substituted with an aryl group having5 to 16 carbon atoms include diphenylamino group, ditolylamino group,dinaphthylamino group and naphthylphenylamino group.

[0068] Examples of the ester group having 1 to 6 carbon atoms includemethoxycarbonyl group, ethoxycarbonyl group, propoxycarbonyl group andisopropoxycarbonyl group.

[0069] Examples of the halogen atom include fluorine atom, chlorine atomand bromine atom.

[0070] Examples of the aryl group include styrylphenyl group,styrylbiphenyl group and styrylnaphthyl group.

[0071] Preferable examples of the anthracene derivative represented bygeneral formula (5) include anthracene derivatives represented bygeneral formula (5-a):

[0072] wherein R⁷¹ to R⁷⁶ each independently represent an alkyl group, acycloalkyl group, an alkenyl group, a substituted or unsubstituted arylgroup, an alkoxyl group, an aryloxyl group, an alkylamino group, anarylamino group or a substituted or unsubstituted heterocyclic group; aand b each represent an integer of 0 to 5; c, d, e and f each representan integer of 0 to 4; when any of a to f represents an integer of 2 orgreater, a plurality of groups represented by the corresponding R⁷¹,R⁷², R⁷³, R⁷⁴, R⁷⁵ or R⁷⁶ may be the same with or different from eachother and may form a ring by forming a bond between each other; and L¹represents a single bond, —O—, —S—, —N(R)— or an arylene group, Rrepresenting an alkyl group or a substituted or unsubstituted arylgroup; and

[0073] anthracene derivatives represented by general formula (5-b):

[0074] wherein R⁷⁷ to R⁸⁴ each independently represent an alkyl group, acycloalkyl group, an alkenyl group, a substituted or unsubstituted arylgroup, an alkoxyl group, an aryloxyl group, an alkylamino group, anarylamino group or a substituted or unsubstituted heterocyclic group; gand h each represent an integer of 0 to 4; i, j, k and 1 each representan integer of 0 to 5; p and q each represent an integer of 0 to 3; whenany of g to 1 represents an integer of 2 or greater, a plurality ofgroups represented by corresponding R⁷⁷, R⁷⁸, R⁷⁹, R⁸⁰, R⁸¹ or R⁸² maybe the same with or different from each other and may form a ring byforming a bond between each other; and L² represents a single bond, —O—,—S—, —N(R)— or an arylene group, R representing an alkyl group or asubstituted or unsubstituted aryl group.

[0075] In the above general formulae (5-a) and (5-b), preferableexamples of the groups represented by R⁷¹ to R⁸⁴ include alkyl groupshaving 1 to 6 carbon atoms, cycloalkyl groups having 3 to 6 carbonatoms, aryl groups having 5 to 18 carbon atoms, alkoxyl groups having 1to 6 carbon atoms, aryloxy groups having 5 to 18 carbon atoms, aminogroups substituted with an aryl group having 5 to 16 carbon atoms andheterocyclic groups such as triazole group, oxadiazole group,quinoxaline group, furanyl group and thienyl group.

[0076] In the group represented by —N(R)— which is represented by L¹ orL², preferable examples of the group represented by R include alkylgroups having 1 to 6 carbon atoms and aryl groups having 5 to 18 carbonatoms.

[0077] Preferable examples of the anthracene derivative represented bygeneral formula (6) include anthracene derivatives represented bygeneral formula (6-a):

A^(3′)-An-A^(4′)  (6-a)

[0078] wherein An represents a substituted or unsubstituted divalentanthracene residue group and A^(3′) and A^(4′) each independentlyrepresent a monovalent residue group derived from biphenyl,fluoranthene, naphthalene, phenanthrene, anthracene, pyrene, perylene,coronene, chrysene, picene, fluorene, terphenyl, diphenylanthracene,biphenyl, an N-alkylcarbazole, an N-arylcarbazole, triphenylene,rubicene, benzoanthracene or dibenzoanthracene, which may be substitutedor unsubstituted; or a group represented by general formula (6-b):

[0079] wherein B¹ and B² each represent a substituted or unsubstitutedphenyl group, naphthyl group, biphenyl group, terphenyl group or anthrylgroup.

[0080] Examples of the substituent in the groups represented by An,A^(3′) and A^(4′) include the groups described as the examples of thesubstituents in general formulae (5) and (6).

[0081] In the present invention, the anthracene derivative may be usedsingly or in combination of two or more.

[0082] The electron transporting compound used in the organic EL deviceof the present invention may be a cyclic derivative having Si such assilacyclopentadiene derivatives.

[0083] In the organic EL device of the present invention, it ispreferable that the thickness of the layer of the organic light emittingmedium is in the range of 5 to 200 nm and more preferably in the rangeof 10 to 100 nm since the voltage applied to the device can beremarkably decreased.

[0084] By using the combination of component (A) and component (B) forthe layer of the organic light emitting medium, crystallization in thelayer of the organic light emitting medium is suppressed and the layerof the organic light emitting medium becomes more amorphous. Therefore,stability is enhanced and heat resistance is improved. As the compoundof component (B), compounds having a glass transition temperature of110° C. or higher are preferable. By mixing the compound having a glasstransition temperature of 110° C. or higher, the glass transitiontemperature of the layer of the organic light emitting medium can beraised to 110° C. or higher and a heat resistance in storage of 500hours or longer at 85° C. can be obtained.

[0085] The chromaticity and the peak wavelength in the spectrum of theemitted light can, be controlled by adjusting the relative amounts ofcomponent (A) and component (B). By increasing the relative amount ofcomponent (A), the peak wavelength in the spectrum of the emitted lightshifts to longer wavelengths and the x-coordinate of the chromaticitycoordinates increases. This phenomenon takes place because the peakwavelength in the spectrum of emitted light due to component (A) is inthe region of longer wave lengths.

[0086] It is preferable that component (A) and component (B) are mixedin amounts such that the ratio of the amount by weight of component (A)to the amount by weight of component (B) is in the range of 8:92 to92:8. When the amount of component (A) is less than 8% by weight, itbecomes difficult that holes are transported to the area ofrecombination through the lowest occupied orbital of the holetransporting compound. This phenomenon can be found from the increase inthe voltage applied to the device when the amount of component (A) isless than 8%. When the amount of component (A) exceeds 92% by weight, itbecomes difficult that electrons are transported to the area ofrecombination through the lowest unoccupied orbital of the electrontransporting compound. It is preferable that the ratio of the amount byweight of component (A) to the amount by weight of component (B) is inthe range of 15:60 to 85:40 since the device has a longer life.

[0087] In the organic EL device of the present invention, it ispreferable that the mixed layer in the layer of the organic lightemitting medium further comprises (C) a fluorescent compound since heatresistance and the efficiency of light emission are further improved. Itis preferable that the mixed layer of the organic light emitting mediumcomprises components (A), (B) and (C) in amounts such that a ratio of atotal amount by weight of component (A) and component (B) to an amountby weight of component (C) is in the range of 100:1 to 10:1.

[0088] In the organic EL device of the present invention, it ispreferable that various intermediate layers are disposed between theelectrodes and the layer of the organic light emitting medium. Examplesof the intermediate layer include a hole injecting layer, a holetransporting layer, an electron injecting layer and an electrontransporting layer. It is known that various organic and inorganiccompounds can be used for these layers.

[0089] Typical examples of the construction of the organic EL deviceinclude:

[0090] An anode/a layer of an organic light emitting medium/a cathode;

[0091] An anode/a hole injecting layer/a layer of an organic lightemitting medium/a cathode;

[0092] An anode/a layer of an organic light emitting medium/an electroninjecting layer/a cathode;

[0093] An anode/a hole injecting layer/a layer of an organic lightemitting medium/an electron injecting layer/a cathode;

[0094] An anode/an organic semiconductor layer/a layer of an organiclight emitting medium/a cathode;

[0095] An anode/an organic semiconductor layer/an electron barrierlayer/a layer of an organic light emitting medium/a cathode;

[0096] An anode/an organic semiconductor layer/a layer of an organiclight emitting medium/an adhesion improving layer/a cathode; and

[0097] An anode/a hole injecting layer/a hole transporting layer/a layerof an organic light emitting medium/an electron injecting layer/acathode.

[0098] However, the construction of the organic EL device is not limitedto the above examples.

[0099] In general, the organic EL device is prepared on a substratewhich transmits light. The substrate which transmits light is thesubstrate which supports the organic EL device. It is preferable thatthe substrate which transmits light has a transmittance of light of 50%or greater and more preferably 80% or greater in the visible region of400 to 700 nm. It is also preferable that a flat and smooth substrate isused.

[0100] As the substrate which transmits light, for example, glass platesand synthetic resin plates are advantageously used. Specific examples ofthe glass plates include plates made of soda ash glass, glass containingbarium and strontium, lead glass, aluminosilicate glass, borosilicateglass, barium borosilicate glass and quartz. Specific examples of thesynthetic resin plates include plates made of polycarbonate resins,acrylic resins, polyethylene terephthalate resins, polyether sulfideresins and polysulfone resins.

[0101] As the anode, an electrode made of a material such as a metal, analloy, a conductive compound and a mixture of these materials which hasa great work function (4 eV or more) is preferably used. Specificexamples of the material for the anode include metals such as Au andconductive materials such as CuI, ITO (indium tin oxide), SnO₂, ZnO andIn—Zn—O. The anode can be prepared by forming a thin film of theelectrode material described above in accordance with a process such asthe vapor deposition process and the sputtering process. When the lightemitted from the light emitting layer is obtained through the anode, itis preferable that the anode has a transmittance of the emitted lightgreater than 10%. It is also preferable that the sheet resistivity ofthe anode is several hundred Ω/□ or smaller. The thickness of the anodeis, in general, selected in the range of 10 nm to 1 μm and preferably inthe range of 10 to 200 nm although the preferable range may be differentdepending on the used material.

[0102] As the cathode, an electrode made of a material such as a metal,an alloy, a conductive compound and a mixture of these materials whichhas a small work function (4 eV or smaller) is used. Specific examplesof the material for the cathode include sodium, sodium-potassium alloys,magnesium, lithium, magnesium-silver alloys, aluminum/aluminum oxide,Al/Li₂O, Al/LiO₂, Al/LiF, aluminum-lithium alloys, indium and rare earthmetals. The cathode can be prepared by forming a thin film of thematerial described above in accordance with a process such as the vapordeposition process and the sputtering process. When the light emittedfrom the layer of the organic light emitting medium is obtained throughthe cathode, it is preferable that the cathode has a transmittance ofthe emitted light greater than 10%. It is also preferable that the sheetresistivity of the cathode is several hundred Ω/□ or smaller. Thethickness of the cathode is, in general, selected in the range of 10 nmto 1 μm and preferably in the range of 50 to 200 nm although thepreferable range may be different depending on the used material.

[0103] In the organic EL device of the present invention, it ispreferable that a layer of a chalcogenide, a metal halide or a metaloxide (this layer may occasionally be referred to as a surface layer) isdisposed on the surface of at least one of the pair of electrodesprepared as described above. Specifically, it is preferable that a layerof a chalcogenide (including an oxide) of a metal such as silicon andaluminum is disposed on the surface of the anode at the side of thelayer of the organic light emitting medium and a layer of a metal halideor a metal oxide is disposed on the surface of the cathode at the sideof the layer of the organic light emitting medium. Due to the abovelayers, holes or electrons are more easily injected into the lightemitting medium and the device can be driven at a lower voltage.

[0104] Preferable examples of the chalcogenide include SiO_(x) (1≦x≦2),AlO_(x) (1≦x≦1.5), SiON and SiAlON. Preferable examples of the metalhalide include LiF, MgF₂, CaF₂ and fluorides of rare earth metals.Preferable examples of the metal oxide include Cs₂O, Li₂O, MgO, SrO, BaOand CaO.

[0105] In the organic EL device of the present invention, the electrontransporting property and the hole transporting property of the layer ofthe organic light emitting medium are simultaneously improved bysuitably adjusting the relative amounts of component (A) and component(B) described above and the above intermediate layers such as the holeinjecting layer, the hole transporting layer and the electron injectinglayer can be omitted. In this case, it is preferable that the surfacelayer described above is disposed.

[0106] In the organic EL device of the present invention, it ispreferable that a mixed region of an electron transfer compound and areducing dopant or a mixed region of a hole transfer compound and anoxidizing dopant is disposed on the surface of at least one of the pairof electrodes prepared as described above. Due to the mixed regiondisposed on the surface of the pair of electrodes, the electron transfercompound is reduced to form an anion. Injection and transportation ofelectrons from the mixed region into the light emitting medium can befacilitated and the device can be driven at a lower voltage. The holetransfer compound is oxidized to form a cation and injection andtransportation of holes from the mixed region into the light emittingmedium is facilitated. Preferable examples of the oxidizing dopantinclude various types of Lewis acid and acceptor compounds. Preferableexamples of the reducing dopant include alkali metals, compounds ofalkali metals, alkaline earth metals, rare earth metals and compounds ofthese metals.

[0107] In the organic EL device of the present invention, the layer ofthe organic light emitting medium has the following functions:

[0108] (1) The injecting function: the function of injecting holes fromthe anode or the hole injecting layer and injecting electrons from thecathode or the electron injecting layer when an electric field isapplied;

[0109] (2) The transporting function: the function of transportinginjected charges (electrons and holes) by the force of the electricfield; and

[0110] (3) The light emitting function: the function of providing thefield for recombination of electrons and holes and leading therecombination to the emission of light.

[0111] In the organic EL device of the present invention, it ispreferable that the work function WF of the anode which injects holesinto the layer of the organic light emitting medium and the ionizationenergy of the hole transporting compound IP1 satisfy a relation:IP1−WFS≦0.2 eV. When the above relation is satisfied, hole injectionfrom the anode into the light emitting medium is increased and the holeinjection layer can be omitted. Therefore, the device can be simplifiedand the production cost of the device can be reduced.

[0112] As the process for forming the layer of the organic lightemitting medium, a conventional process such as the vapor depositionprocess, the spin coating process and the Langmuir-Blodgett process (theLB process) can be used. It is particularly preferable that the layer ofthe organic light emitting medium is a molecular deposit film. Themolecular deposit film is a thin film formed by deposition of a materialcompound in the gas phase or a thin film formed by solidification of amaterial compound in a solution or in the liquid phase. In general, themolecular deposit film can be distinguished from the thin film formed inaccordance with the LB process (the molecular accumulation film) basedon the differences in the aggregation structure and higher orderstructures and functional differences caused by these structuraldifferences.

[0113] As disclosed in Japanese Patent Application Laid-Open No. Showa57(1982)-51781, the layer of the organic light emitting medium can alsobe formed by dissolving a binder such as a resin and the materialcompounds into a solvent to prepare a solution, followed by forming athin film from the prepared solution in accordance with the spin coatingprocess or the like.

[0114] In the present invention, where desired, conventional lightemitting media other than component (A), component (B) and component (C)described above may be comprised in the layer of the organic lightemitting medium or a layer of an organic light emitting mediumcomprising other conventional light emitting media may be laminated tothe layer of the organic light emitting medium comprising the compoundsdescribed in the present invention as long as the object of the presentinvention is not adversely affected.

[0115] The hole injecting layer and the hole transporting layer arelayers which help injection of holes into the layer of the organic lightemitting medium and transport the holes to the light emitting region.The layers exhibit a great mobility of holes and, in general, have anionization energy as small as 5.5 eV or smaller. For the hole injectinglayer and the hole transporting layer, a material which transports holesto the layer of the organic light emitting medium at a small electricfield strength is preferable. A material which exhibits, for example, amobility of holes of at least 10⁻⁶ cm²/V·sec under application of anelectric field of 10⁴ to 10⁶ V/cm is more preferable. A material can beselected from materials which are conventionally used as the chargetransporting material of holes in photoconductive materials andconventional materials which are used for the hole injecting layer inorganic EL devices.

[0116] To form the hole injecting layer or the hole transporting layer,a thin film may be formed from a material substance for the holeinjecting layer or the hole transporting layer, respectively, inaccordance with a conventional process such as the vacuum vapordeposition process, the spin coating process, the casting process andthe LB process. The thickness of the hole injecting layer and the holetransporting layer is not particularly limited. In general, thethickness is 5 nm to 5 μm.

[0117] The electron injection layer is a layer which helps injection ofelectrons into the layer of the organic light emitting medium andexhibits a great mobility of electrons. The adhesion improving layer isa layer made of a material exhibiting excellent adhesion with thecathode in the electron injecting layer. As the material for theelectron injecting layer, metal complexes of 8-hydroxyquinoline andderivatives thereof are preferably used. Specific examples of the metalcomplex of 8-hydroxyquinoline and derivatives thereof include metalchelates of oxinoid compounds including chelates of oxine (in general,8-quinolinol or 8-hydroxyquinoline). For example,tris(8-quinolinol)aluminum can be used as the electron injectingmaterial.

[0118] To prepare the organic EL device of the present invention, forexample, the anode, the layer of the organic light emitting medium and,where necessary, the hole injecting layer and the electron injectinglayer are formed in accordance with the above process using the abovematerials and the cathode is formed in the last step. The organic ELdevice may be prepared by forming the above layers in the order reverseto that described above, i.e., the cathode being formed in the firststep and the anode in the last step.

[0119] An embodiment of the process for preparing an organic EL devicehaving a construction in which an anode, a hole injecting layer, a layerof the organic light emitting medium, an electron injecting layer and acathode are disposed successively on a substrate which transmits lightwill be described in the following.

[0120] On a suitable substrate which transmits light, a thin film madeof a material for the anode is formed in accordance with the vapordeposition process or the sputtering process so that the thickness ofthe formed thin film is 1 μm or smaller and preferably in the range of10 to 200 nm. The formed thin film is used as the anode. Then, a holeinjecting layer is formed on the anode. The hole injecting layer can beformed in accordance with the vacuum vapor deposition process, the spincoating process, the casting process or the LB process, as describedabove. The vacuum vapor deposition process is preferable because auniform film can be easily obtained and the possibility of formation ofpin holes is small. When the hole injecting layer is formed inaccordance with the vacuum vapor deposition process, in general, it ispreferable that the conditions are suitably selected in the followingranges: the temperature of the source of the deposition: 50 to 450° C.;the vacuum: 10⁻⁷ to 10⁻³ Torr; the rate of deposition: 0.01 to 50nm/second; the temperature of the substrate: −50 to 300° C. and thethickness of the film: 5 nm to 5 μm; although the conditions of thevacuum vapor deposition are different depending on the used compound(the material for the hole injecting layer) and the crystal structureand the recombination structure of the hole injecting layer to beformed.

[0121] Then, the layer of the organic light emitting medium is formed onthe hole injecting layer formed above. Using the organic light emittingmedium described in the present invention, a thin film of the organiclight emitting medium can be formed in accordance with the vacuum vapordeposition process, the sputtering process, the spin coating process orthe casting process and the formed thin film is used as the layer of theorganic light emitting medium. The vacuum vapor deposition process ispreferable because a uniform film can be easily obtained and thepossibility of formation of pin holes is small. When the layer of theorganic light emitting medium is formed in accordance with the vacuumvapor deposition process, in general, the conditions of the vacuum vapordeposition process can be selected in the same ranges as those describedfor the vacuum vapor deposition of the hole injecting layer although theconditions are different depending on the used compound. It ispreferable that the thickness is in the range of 10 to 40 nm.

[0122] An electron injecting layer is formed on the layer of the organiclight emitting medium formed above. Similarly to the hole injectinglayer and the layer of the organic light emitting medium, it ispreferable that the electron injecting layer is formed in accordancewith the vacuum vapor deposition process since a uniform film must beobtained. The conditions of the vacuum vapor deposition can be selectedin the same ranges as those described for the vacuum vapor deposition ofthe hole injecting layer and the layer of the organic light emittingmedium.

[0123] A cathode is formed on the electron injecting layer formed abovein the last step and an organic EL device can be obtained. The cathodeis made of a metal and can be formed in accordance with the vacuum vapordeposition process or the sputtering process. It is preferable that thevacuum vapor deposition process is used in order to prevent formation ofdamages on the lower organic layers during the formation of the film.

[0124] In the above preparation of the organic EL device, it ispreferable that the above layers from the anode to the cathode areformed successively while the preparation system is kept in a vacuumafter being evacuated.

[0125] The organic EL device which can be prepared as described aboveemits light when a direct voltage of 3 to 40 V is applied in thecondition that the anode is connected to a positive electrode (+) andthe cathode is connected to a negative electrode (−). When theconnection is reversed, no electric current is observed and no light isemitted at all. When an alternating voltage is applied to the organic ELdevice, light emission is observed only in the condition that thepolarity of the anode is positive and the polarity of the cathode isnegative. When an alternating voltage is applied to the organic ELdevice, any type of wave shape can be used.

[0126] The present invention will be described more specifically withreference to examples in the following. However, the present inventionis not limited to the examples.

EXAMPLE 1 The Ratio of Amounts by Weight: 40:20

[0127] On a glass plate having a size of 25×75×1.1 mm, a transparentelectrode made of indium tin oxide and having a thickness of 120 nm wasformed. After the glass substrate was cleaned by irradiation withultraviolet light and exposure to ozone, the glass substrate was placedin a vacuum vapor deposition apparatus.

[0128] In the first step, TPD106 expressed by the following formula:

[0129] was vapor deposited so that a layer having a thickness of 60 nmwas formed. Then, TPD78 expressed by the following formula:

[0130] was vapor deposited on the formed layer so that a holetransporting layer having a thickness of 20 nm was formed on the layerof TPD106. Then, DC5 expressed by the following formula:

[0131] DC5: a mixture of isomers in a ratio of amounts of 70/30.

[0132] as the hole transporting compound and Alq (an Al complex of8-hydroxyquinoline) as the electron transporting compound weresimultaneously vapor deposited on the formed layers in amounts such thatthe ratio of the amount by weight of DC5 to the amount by weight of Alqwas 67.7:32.3 and a layer of an organic light emitting medium having athickness of 40 nm was formed. Then, Alq was vapor deposited so that alayer having a thickness of 20 nm was formed on the layer formed aboveas the electron injecting layer.

[0133] The energy gap of DC5 (Eg1) is 2.57 eV and smaller than theenergy gap (Eg2) of Alq which is 2.7 eV. The ionization energy of DC5(IP1) is 5.6 eV and smaller than the ionization energy (IP2) of Alqwhich is 5.7 eV. The electron affinity of DC5 (Af1) is 3.0 eV and thesame as the electron affinity (Af2) of Alq which is 3.0 eV.

[0134] Then, LiF which was an alkali metal halide was vapor deposited sothat a layer having a thickness of 0.3 nm was formed on the above layersand aluminum was vapor deposited so that a layer having a thickness of100 nm was formed on the layer of LiF. The layers of LiF and Al workedas the cathode. An organic EL device was prepared as described above.

[0135] The prepared organic EL device was tested by passing an electriccurrent. Reddish orange light emission having a luminance of 110 cd/m²was obtained at a voltage of 4.5 V and a current density of 2.46 mA/cm².The chromaticity coordinates were (0.6039, 0.3931) and the efficiency oflight emission was 4.47 cd/A. The device was tested by continuouslypassing a current constantly at an initial luminance of 500 cd/m² andthe half-life time was found to be as long as 3,120 hours.

EXAMPLE 2

[0136] An organic EL device was prepared in accordance with the sameprocedures as those conducted in Example 1 except that DC5 and Alq wereused for forming the layer of an organic light emitting medium inamounts such that the ratio of the amount by weight of DC5 to the amountby weight of Alq was 44.4:55.6.

[0137] The prepared organic EL device was tested by passing an electriccurrent. Red light emission having a luminance of 109 cd/M² was obtainedat a voltage of 4.0 V and a current density of 2.71 mA/cm². Thechromaticity coordinates were (0.5886, 0.4072) and the efficiency oflight emission was 4.02 cd/A. The device was tested by continuouslypassing a current constantly at an initial luminance of 500 cd/m² andthe half-life time was found to be as long as 3,760 hours.

EXAMPLE 3

[0138] An organic EL device was prepared in accordance with the sameprocedures as those conducted in Example 1 except that DC5 and Alq wereused for forming the layer of an organic light emitting medium inamounts such that the ratio of the amount by weight of DC5 to the amountby weight of Alq was 28.6:71.4.

[0139] The prepared organic EL device was tested by passing an electriccurrent. Red light emission having a luminance of 124 cd/m² was obtainedat a voltage of 4.0 V and a current density of 2.96 mA/cm². Thechromaticity coordinates were (0.5741, 0.4228) and the efficiency oflight emission was 4.19 cd/A. The device was tested by continuouslypassing a current constantly at an initial luminance of 500 cd/m² andthe half-life time was found to be as long as 4,100 hours.

EXAMPLE 4

[0140] An organic EL device was prepared in accordance with the sameprocedures as those conducted in Example 1 except that DC5 and Alq wereused for forming the layer of an organic light emitting medium inamounts such that the ratio of the amount by weight of DC5 to the amountby weight of Alq was 12:88.

[0141] The prepared organic EL device was tested by passing an electriccurrent. Red light emission having a luminance of 135 cd/m² was obtainedat a voltage of 4.5 V and a current density of 3.0 mA/cm². Thechromaticity coordinates were (0.5652, 0.4352) and the efficiency oflight emission was 4.50 cd/A. The device was tested by continuouslypassing a current constantly at an initial luminance of 500 cd/m² andthe half-life time was found to be as long as 2,900 hours.

COMPARATIVE EXAMPLE 1

[0142] An organic EL device was prepared in accordance with the sameprocedures as those conducted in Example 1 except that DC5 and Alq wereused for forming the layer of an organic light emitting medium inamounts such that the ratio of the amount by weight of DC5 to the amountby weight of Alq was 2.4:97.6.

[0143] The prepared organic EL device was tested by passing an electriccurrent. A current of 1.30 mA/cm² was observed at a voltage of 6 V. Theapplied voltage was higher than those for the organic EL devices ofExamples 1 to 4. The luminance was 173 cd/m², the chromaticitycoordinates were (0.5416, 0.4550) and the efficiency of light emissionwas 8.78 cd/A. The purity of red light was insufficient in comparisonwith those in Examples 1 to 4. The device was tested by continuouslypassing a current constantly at an initial luminance of 500 cd/m² andthe half-life time was found to be 970 hours. The half-life was muchshorter than those in Examples 1 to 4.

COMPARATIVE EXAMPLE 2

[0144] An organic EL device was prepared in accordance with the sameprocedures as those conducted in Example 1 except that DC5 and Alq wereused for forming the layer of an organic light emitting medium inamounts such that the ratio of the amount by weight of DC5 to the amountby weight of Alq was 4.8:95.2.

[0145] Using the prepared organic EL device, the voltage showing thesame luminance as that of the device of Comparative Example 1 wasmeasured and found to be 7.3 V. The voltage was higher than that of thedevice of Comparative Example 1.

COMPARATIVE EXAMPLE 3

[0146] An organic EL device was prepared in accordance with the sameprocedures as those conducted in Example 1 except that DC5 and Alq wereused for forming the layer of an organic light emitting medium inamounts such that the ratio of the amount by weight of DC5 to the amountby weight of Alq was 9.1:90.9.

[0147] Using the prepared organic EL device, the voltage showing thesame luminance as that of the device of Comparative Example 1 wasmeasured and found to be 7.1 V. The voltage was higher than that of thedevice of Comparative Example 1.

[0148] It can be concluded from the results in Comparative Examples 2and 3 that Alq worked as the trap for holes transported from DC5 and theapplied voltage increased. In contrast, devices in which DC5 was addedin an amount exceeding 10% by weight showed a remarkable decrease in thevoltage. It can be concluded that the voltage decreased since DC5 workedas a compound having the hole transporting property and holes could betransported at a high efficiency.

COMPARATIVE EXAMPLE 4

[0149] An organic EL device was prepared in accordance with the sameprocedures as those conducted in Example 1 except that TPD(N,N′-bis(m-methylphenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine)having an energy gap (Eg1) of 3.0 eV was used in place of DC5.

[0150] The prepared organic EL device was tested by passing an electriccurrent. Green light emission having a luminance of 56 cd/m² wasobtained at a voltage of 5.6 V and a current density of 2.8 mA/cm². Theefficiency of light emission was 2.0 cd/A. The device was tested bycontinuously passing a current constantly at an initial luminance of 500cd/m² and the half-life time was found to be as short as 130 hours.Therefore, the device in Example 1 was superior to the device inComparative Example 4 with respect to both of the efficiency of lightemission and the life. Thus, it is shown that an organic EL device inthe condition of Eg1≧Eg2 has a problem in practical applications.

[0151] Industrial Applicability

[0152] As described in detail in the above, in accordance with thepresent invention, the organic EL device having a longer life andemitting light at a higher efficiency than those of conventional ELdevices can be obtained. The organic EL device of the present inventioncan be advantageously used, for example, for displays of informationinstruments.

1. An organic electroluminescence device comprising a pair of electrodesand a layer of an organic light emitting medium disposed between thepair of electrodes, wherein the layer of an organic light emittingmedium comprises a mixed layer consisting essentially of (A) at leastone compound selected from hole transporting compounds and (B) at leastone compound selected from electron transporting compounds in amountssuch that a ratio of an amount of component (A) to an amount ofcomponent (B) is in a range of 28.6:71.4 to 44.4:55.6 and an energy gapof the hole transporting compound represented by Eg1 and an energy gapof the electron transporting compound represented by Eg2 satisfy arelation: Eg1<Eg2.
 2. An organic electroluminescence device according toclaim 1, wherein an ionization energy of the hole transporting compoundrepresented by IP1 and an ionization energy of the electron transportingcompound represented by IP2 satisfy a relation: IP1≦IP2.
 3. An organicelectroluminescence device according to claim 2, wherein an electronaffinity of the hole transporting compound represented by Af1 and anelectron affinity of the electron transporting compound represented byAf2 satisfy a relation: Af1≦Af2 and ΔEv given by ΔEv=IP2−IP1 and ΔEcgiven by ΔEc=Af2−AF1 satisfy a relation: ΔEv=Ec.
 4. An organicelectroluminescence device according to claim 2, wherein an electronaffinity of the hole transporting compound represented by Af1 and anelectron affinity of the electron transporting compound represented byAf2 satisfy a relation: Af1>Af2 and ΔEv given by ΔEv=IP2−IP1 and ΔEcgiven by ΔEc′=Af1−AF2 satisfy a relation: ΔEv≧Ec′.
 5. An organicelectroluminescence device according to claim 1, wherein the holetransporting compound is an aromatic amine having condensed cyclicstructures.
 6. An organic electroluminescence device according to claim5, wherein the aromatic amine is represented by following generalformula (1):

wherein Ar¹ to Ar⁴ each independently represent a substituted orunsubstituted aromatic hydrocarbon group having 6 to 40 carbon atoms ora substituted or unsubstituted aromatic heterocyclic group having 3 to40 carbon atoms, Y represents a substituted or unsubstituted aromaticresidue group having 2 to 60 carbon atoms, at least one of the groupsrepresented by Ar¹ to Ar⁴ and Y has a condensed cyclic group having 3 ormore rings and a substituent in the groups represented by Ar¹ to Ar⁴ andY may form a ring with two groups selected from the groups representedby Ar¹ to Ar⁴ and Y.
 7. An organic electroluminescence device accordingto claim 5, wherein the aromatic amine is represented by followinggeneral formula (2):

wherein Ar¹ to Ar⁶ each independently represent a substituted orunsubstituted aromatic hydrocarbon group having 6 to 40 carbon atoms ora substituted or unsubstituted aromatic heterocyclic group having 3 to40 carbon atoms, Z represents a substituted or unsubstituted aromaticresidue group having 3 to 60 carbon atoms, at least one of the groupsrepresented by Ar¹ to Ar⁶ and Z has a condensed cyclic group: having 3or more rings and a substituent in the groups represented by Ar¹ to Ar⁶and Z may form a ring with two groups selected from the groupsrepresented by Ar¹ to Ar⁶ and Z.
 8. An organic electroluminescencedevice according to claim 1, wherein the electron transporting compoundis a heterocyclic compound having a nitrogen atom or a complex having anitrogen atom.
 9. An organic electroluminescence device according toclaim 8, wherein the complex having a nitrogen atom is represented byfollowing general formula (3): M-A_(m)B_(n)   (3) wherein M represents amonovalent to trivalent metal, A represents a ligand having a nitrogenatom, B represents a ligand having no nitrogen atoms, m represents aninteger of 1 to 4, n represents an integer of 0 to 2 and integersrepresented by m and n satisfy m+n≦4.
 10. An organic electroluminescencedevice according to claim 9, wherein the ligand having a nitrogen atomis represented by following general formula (4):

wherein R² to R⁷ each independently represent hydrogen atom, a halogenatom, hydroxyl group, a substituted or unsubstituted amino group, nitrogroup, cyano group, a substituted or unsubstituted alkyl group having 1to 30 carbon atoms, a substituted or unsubstituted alkenyl group having2 to 30 carbon atoms, a substituted or unsubstituted cycloalkyl grouphaving 5 to 30 carbon atoms, a substituted or unsubstituted alkoxylgroup having 1 to 30 carbon atoms, a substituted or unsubstitutedaromatic hydrocarbon group having 6 to 40 carbon atoms, a substituted orunsubstituted aromatic heterocyclic group having 3 to 40 carbon atoms, asubstituted or unsubstituted aralkyl group having 7 to 40 carbon atoms,a substituted or unsubstituted aryloxyl group having 6 to 40 carbonatoms, a substituted or unsubstituted alkoxycarbonyl group having 2 to40 carbon atoms or carboxyl group and two groups selected from thegroups represented by R² to R⁷ may form a ring.
 11. An organicelectroluminescence device according to claim 1, wherein the electrontransporting compound is represented by following general formula (5):A¹-L-A²   (5) wherein A¹ and A² each independently represent asubstituted or unsubstituted monophenylanthryl group or a substituted orunsubstituted diphenylanthryl group and may represent a same group ordifferent groups and L represents a single bond or a divalent bondinggroup; or by following general formula (6): A³-An-A⁴   (6) wherein Anrepresents a substituted or unsubstituted anthracene residue group andA³ and A⁴ each independently represent a substituted or unsubstitutedmonovalent condensed aromatic cyclic group having 10 to 40 carbon atomsor a substituted or unsubstituted aryl group having no condensed cyclicstructures and having 12 to 40 carbon atoms and may represent a samegroup or different groups.
 12. An organic electroluminescence deviceaccording to claim 1, wherein the electron transporting compound is acyclic derivative having Si.
 13. An organic electroluminescence deviceaccording to claim 1, wherein the mixed layer in the layer of an organiclight emitting medium further comprises (C) a fluorescent compound. 14.An organic electroluminescence device according to claim 13, wherein thelayer of an organic light emitting medium comprises component (A),component (B) and component (C) in amounts such that a ratio of a totalamount by weight of component (A) and component (B) to an amount byweight of component (C) is in a range of 100:1 to 10:1.
 15. An organicelectroluminescence device according to claim 1, wherein a layer of achalcogenide, a metal halide or a metal oxide is disposed on a surfaceof at least one of the pair of electrodes.
 16. An organicelectroluminescence device according to claim 1, wherein a mixed regionof a reducing dopant and the electron transporting compound or a mixedregion of an oxidizing dopant and the hole transporting compound isdisposed on a surface of at least one of the pair of electrodes.
 17. Anorganic electroluminescence device according to claim 1, wherein a workfunction WF of an anode which injects holes into the layer of an organiclight emitting medium and an ionization energy of the hole transportingcompound IP1 satisfy a relation: IP1−WF≦0.2 eV.
 18. An organicelectroluminescence device comprising a pair of electrodes and a layerof an organic light emitting medium disposed between the pair ofelectrodes, wherein the layer of an organic light emitting mediumcomprises a mixed layer consisting essentially of (A) at least onecompound selected from hole transporting compounds in amounts such thata ratio of an amount of component (A) to an amount of (B) is in a rangeof 8:92 to 44.4:55.6 and (B) at least one compound selected fromelectron transporting compounds in amounts such that a ratio of anamount of component (A) to an amount of component (B) is in a range of28.6:71.4 to 44.4 to 55.6 and an energy gap of the hole transportingcompound represented by Eg1 and an energy gap of the electrontransporting compound represented by Eg2 satisfy a relation: Eg1<Eg2 andholes are transported in the layer of an organic light emitting mediumwith the hole transporting compound.